A busway as used in an electrical distribution system, which can include a switchboard, switchgear, or motor-control center, includes a housing enclosing a stack of insulated electrical phase conductors called busbars, in prefabricated sections. The sections are joined together to carry the different phases of electrical current from a source of energy to one or more loads. The conductors are typically made of copper and can carry hundreds or even thousands of amperes of current. As a result, these conductors get very hot and efforts are made to cool them so that they meet thermal requirements set by a certification organization such as Underwriters Laboratory (UL). One way to cool conductors is to add more copper by making them thicker or wider, but copper is expensive and more of it adds bulkiness and heft to the busway overall.
There are two types of busways, feeder busways and plug-in busways. Feeder busways feed long (e.g., up to ten feet) straight sections of current, while plug-in busways allow for connections, typically in a perpendicular manner, to the long sections of the busways, to route the current to other areas of an electrical distribution system. To allow for connections to the plug-in busways, some busbar conductors in plug-in busways have flared-out sections to accommodate the busbar conductors from the connections. These flared-out sections create relatively larger air gaps between the busbar conductors so that the connections can fit snugly in between the air gaps to create electrical connections to each phase. The busbar conductors become particularly hot in the areas near points of contact. This is generally because of additional contact resistance at the points of contact which generate increased power losses at the points of contact. The increased power loss coupled with the thermal resistances for the busway system usually cause an increase in temperature at the points of contact.
Multiple busway sections can be connected together using joint packs, which are metal housings with insulated conductive fingers that receive the ends of busbar conductors from different busway sections. As above, the end of each busway section is flared to allow joining These joint packs can also become very hot as they transfer electrical current from one busway to the next. To meet UL or other certification requirements, a certain amount of copper or conductive material needs to be used to ensure that during normal operating conditions the temperatures of the busbar conductors and joint packs do not exceed rated requirements. If the temperature of the busbar conductors and/or the joint packs can be reduced, less copper can be used in both the busbar conductors and the joint packs, which reduces weight and bulk as well as cost, as long as the cost of a thermal mitigation solution does not exceed the cost of the copper reduction.
One specific type of busway is a horizontally mounted busway with a cross-sectional shape having an H-shaped configuration. By way of example, numerous busway manufacturers use an H-shaped configuration on busways rated for 800+ amperes. As mentioned above, busbars generate heat under normal operating conditions due to inherent internal resistance. In addition to the heat generation discussed above, busways with H-shaped configurations create a cavity on the underside where hot air stratifies and decreases the ability of the busway to transfer heat to the environment. This has the undesired effect of further increasing the operating temperature of the busway.
Thus, a need exists for an improved thermal management system for a busway to lower temperatures along the busway under normal operating conditions.